For years food scientists have had a continuing interest in producing palatable, nutritious proteinaceous food products from plant sources as a supplement to or as a replacement for animal protein foods. The proteinaceous products must be economical, nutritionally well balanced and aesthetically acceptable to the human consumer, i.e., the product must be bland in flavor and odor and must be free of objectionable colors. At the present time, such proteinaceous food products are principally prepared from soybeans. Unfortunately, the soy proteins are relatively deficient in some essential sulfur bearing amino acids.
It is well known that many of the inherent disadvantages of soybeans can be overcome by combining the soy protein with proteins from another source. For example, the protein from cereal grain has an amino acid composition which compliments the amino acid composition of soy protein, i.e., the amino acids which are low in soy protein are high in the cereal grains. Thus, because of their low cost and nutritional value, the crude grain glutens from such cereals as corn, sorghum, wheat and the like have been frequently suggested as having potential use, in combination with soy protein, in food products. In particular, it has been suggested to use corn gluten. Major obstacles, however, to the general use of crude grain gluten have been the characteristic bad flavors and odors, intense colors, oils, and high moisture contents of these potential sources.
Considerable efforts have been made in the past to prepare protein products from grain gluten using classical methods, but such efforts have been only moderately successful. These efforts have not allowed the valuable protein to be recovered in commercial quantities at low cost or completely free of the gluten's characteristic flavors, odors, colors, carbohydrates or salts.
Generally, the classical methods of extraction using linear hydrocarbon solvents have not been satisfactory due to the immiscibility of the solvents with the high amounts of water usually present in the grain gluten. Hydrophilic solvents, such as the lower aliphatic alcohols, have also been used for deoiling oilseeds, but they cannot be used successfully with aqueous wet gluten without serious loss of the alcohol soluble protein fraction. The combination of aqueous alkaline extraction and solvent extraction of cereal grain materials such as corn germ, described by Nielsen et al. in Food Engineering, April 1973, p. 76-77, or such as ground corn having normal and high contents of lysine, described by Wu et al., J. Food Sci. 41:509-512 (1976), has been moderately successful to produce corn concentrates or isolates. Such processes, however, require organic solvent extraction either before or after the aqueous alkaline extraction which is costly or they require highly alkaline aqueous extraction which may nutritionally damage the protein. Aqueous processes such as described by Rhee et al. in J. Food Sci. 37:90 (1972) and J. Food Sci. 38:126 (1973) have been moderately successful for simultaneously recovering protein and oil from peanuts. This process, however, requires that the oilseed be finely ground before processing to achieve good recovery of protein and oil. Such pregrinding of crude grain gluten would be costly and time consuming. Thus, in each case, the prior art techniques are costly and time consuming, and the products which result are not completely satisfactory.